Agitating tank for liquids



Dec. 6, 1938. s wl JR 2,139,430

AGITA'IING TANK FOR LIQUIDS Filed Oct. 25, 1937 3 Sheets-Sheet l 2 Inventor Gear 7e S. Mfham Jr:

Attorn eqs Dec. 6, 1938. s, w A JR 2,139,430

AGITATING TANK FOR LIQUIDS Filed Oct. 25, v193'? 3 Sheets-Sheet 2 I Fiy. 5

I," A 7"... I "1 F117. 4 inventor Georye 51 Wz'tham Jr:

Httorn eys Dec. 6, 1938. G, s, w A JR 2,139,430

AGITATING TANK FOR LIQUIDS Filed Oct. 25, 193'? 5 Sheets-Sheet 3 Inventor Gear 7e 5. Wjzham Jr:

A ttorneys Patented Dec. 6, 1938 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to means for agitating 'iquid in a tank and is designed for tanks used for mixing pulp in the process of paper manufacture, or for mixing chemicals in solution. The

invention concerns the treatment of pulp, or the treatment of any liquid requiring circulating and agitating in tanks, vats, tubs, etc., of any capacity.

Referring specifically to the use of my invention in connection with the treatment of pulp,

when pulp in the ordinary liquid state is maintained or mixed in tanks or tubs, the pulp must be kept in constant circulation or agitation, or else the pulp fibers, which will ordinarily float in water, will have the tendency to collect in masses 16 at the top which prevents proper mixing and treating of the pulp at this point of the process.

This problem increases with the increased height.

or depth of tanks or tubs. On the other hand, due to the desirability-0f economizing floor space and to structural advantages and economies, it is desirable to maintain the pulp during this period in large tanks, preferably cylindrical in shape, and of considerable height.

One of the means which has been tried for as keeping pulp in proper circulation in tanks of any height has been the setting up of a circulating propeller on a vertical axis close to the bottom of the tank. This has not been found entirely satisfactory and has also involved some difliculties of construction, Another means which has been invented for causing proper agitation and circulation in a high tank is a series of pumps located in the tank at different levels.

I have found it is possible, however, to meet the problem more eificiently without the necessity of establishing such circulating means at different levels in the tank. The object of my invention is accordingly to provide a simple means, located at a single level, for producing this necessary agitation and circulation of liquid in a tank.

Another object of my invention is to provide means of this type to be located at the bottom of the tank and so arranged that it will function emciently regardless of the level of the liquid in the tank.

These objects I attain by providing the propeller or circulating means Within the tank, adjacent the bottom thereof, and associated with a mid-feather; and by combining with this circulating means an inclined bevel or back-fall which will act so as to force the circulating current produced in the liquid within the tank to include the upper surface of the liquid in its path at all times.

The manner in which I carry out my invention and accomplish these and incidental objects will be apparent from the following description with reference to the accompanying drawings.

In the drawings:

Fig. 1 is a sectional plan on the line l--l Fig. 2;

Fig. 2 is a sectional elevation on the line 2-2 of Fig. 1;

Fig. 3 is a sectional plan on the line 33 of Fig. 4 illustrating a modification in construction;

Fig. 4 is a sectional elevation on the line 4-4 of Fig. 3; and

Fig. 5 is a partial sectional elevation corresponding to Fig. 2 but showing an alternative circulating means.

Referring first to the form of my invention as illustrated in Figs. 1 and. 2, the outer wall of the tank is indicated by I. I have shown the tank as substantially cylindrical, which I consider the preferred shape. The tank also includes a dome top 2, inclined floor 3 and suitable supporting base 4. The interior'of the tank is provided with a divided partition or mid-feather 5 comprising an end wall 6 and curved side walls I and 8, which extends the full height of the tank and forms a rigid structure of horse-shoe shaped cross-section, as illustrated in Fig. 1. The midfeather 5 is preferably so placed that the center line distance between the end wall 6 thereof and the adjacent portion of the outer wall I is considerably less than the distance from the extremities 9 and Ill of the curved walls 1 and 8, respectively, to the adjacent portion of the outer wall I; thus the passages II and I2 are formed between the curved walls land 8 and the outer wall, which passages gradually decrease in width as they approach the end wall 6 of the midfeather where these passages converge.

The end wall 6 of the mid-feather" has a circular aperture at the base in-which is located the impeller or circulating element. This circulating element preferably comprises a propeller I4 mounted on a horizontal shaft H. The shaft l1 passes through the outer wall of the tank and is journaled in suitable bearings such as indicated at l8, l9 and I9. This shaft I1 is in axial alinement with the longitudinal center line of the mid-feather. Any suitable means for providing a fluid tight joint at the wall bearing I9 may be employed. The shaft l1, and with it the propeller l4, are driven by any suitable means, for example by a motor indicated at l5.

Curving upwardly from the base at the bottom of the end wall 6 and within the space of the mid-feather is a cattle or back-fall 20 which 22 which is recessed in the floor of the tank and in which is located the tank outlet pipe 23. Thus the entire fluid contents of the tank may be drained by gravity.

The tank wall I is preferably formed with an internal vertical ridge or diverging baille N, in alinement with the longitudinal center of the\ mid-feather and equi-distant from the ends 0 and ll of the walls I and I of the divided midfeather", as shown in Fig. l.

The inlet pipe for the tank is preferably located in the domed cover 2 above the propeller shaft II and between the end wall 6 of the midfeather" and the outer wall of the tank, as shown in Fig. 2, so that the pulp entering the tank will be drawn down by the action of the propeller l4 and into the interior of the tank thru the aperture in the base of the wall 6.

Due to the upwardly curving slope of the face of the back-fall" 20, opposite the propeller ll, the pulp drawn thru the aperture in the wall 6 by the action of the propeller will be forced upwardly as well as forward in the tank, and will follow the course indicated by the arrow in Fig. 2 and subsequently by the arrows in Fig. 1. Thus the resultant effect brought about by the upwardly sloping face of the back-fall" is to cause circulation and agitation of the top surface of the liquid in the'tank as well as thruout the other portions of the liquid. This constant circulation of the water and pulp thruout the entire volume of the liquid prevents any collection of the pulp fibers in the form of so-called curds or islands of pulp fibers in the top of the tank'and similar settling of the water at the bottom of the tank. As the pulp, due to the combined influence of the propeller H andthe sloping surface of the backfall 20, is forced upward and forward in the space within the divided "mid-feather, the current is divided by the diverging baffle l3 and part directed thru the passageway l2 and part thru the passageway l I to the opposite side of the tank when it is again drawn thru the aperture in wall 8 by the action of the propeller. The decreasing width of the passageways II and I! retards this flow of the pulp and consequently enhances the downward surging action caused by the suction of the pulp again thru the aperture at the base ofwall 6.

The modified form of my invention shown in Figs. 3 and 4 is similar in construction and operation to that shown in Figs. 1 and 2 but a substitution of two propellers and two back-falls of difl'erent heights is provided for the purpose of obtaining still greater agitation of the pulp in the tank. In this modification the wall 6 of the mid-feather" has two apertures at the base for the purpose of accommodating two propellers and 25, which are mounted on parallel shafts and driven by motors 26 and 26' or by any other suitable means. In place of the single "backfall" 20 of Figs. 1 and 2 I provide two back-falls" 21 and 2], in alinement with each other and each extending half the distance across the space between the curved mid-feather walls 8 and I.

The slopes of the faces of these two back-falls" opposite the propellers are similar and the sur-,

faces coincide, but back-fall 21' is preferably made to extend approximately twice the height of the back-fall 21. With this modified construction I obtain a greater upward surge in half of the space within the "mid-feather, than in the other half, which I have found results in a greater mixing action within the "mid-feather, which is desirable particularly for high tanks and tanks with larger capacities where the propellers are located at considerable depth below the top surface of the pulp. In all other respects the results obtained are similar to those already described with reference to the construction illustrated by Figs. 1 and '2.

Referring now to Fig. 5, a rotary pump 28 may be used as a circulating and agitating means instead of the motor driven impellers of the previous embodiments. The fluid in the tank is drained by gravity into the sump 28 provided in the sloped'fioor 3 of the tank and connected with a pipe line 30 leading to the pump 28. A branch pipe 30. controlled by a stop valve 3| provides a means for withdrawing pulp from the tank or for draining the tank when the pump is not in use. With the valve II closed and the pump 28 operating, the fluid is drawn from the tank into the pipe Ill and then forced back under hizh pressure into the said tank thru a pipe 32 which passes thru the outer tank wall I and is disposed in an aperture of suitable size provided in the partition end wall 6 substantially as shown. The same results is thus obtained as with the agitating elements previously mentioned, the fluid exhausting at high velocity from the return pipe 32 against the back-fall 20 causing upward surging and constant surface agitation. With this modified form of my invention there is the advantage of having the circulating medium located outside of the tank, making it possible to repair the circulating medium without draining the tank.

While it. would be possible to increase the number of apertures and propellers located at the bottom of the mid-feather" wall 8, in my opinion nothing would be gained by so doing, and I have found that one or two propellers, of proper diameter, pitch, and speed, in combination with a back-fall or back-falls, as the case may be, arranged'substantially as I have indicated, will prove ample and efficient for tanks of all practical capacity. Although I have described my invention chiefly in connection with a tank containing pulp, its use would be the same with any liquid materials. The tank which I have shown in the illustrations is circular or cylindrical, but it is obvious that an elliptical or even a rectangular tank might be substituted. Also obviously other modifications might be made in the construction, such as changes in the shape and position of the mid-feather, without departing from the principle of my invention. It is not my intention to limit myself to any particular construction provided that the essential features, namely, an impelling means in combination with upwardly sloping "back-fall" of suflicient height are located at or near the bottom of the tank.

I claim:

1. In a tank for materials in liquid form a mid-feather partition, a plurality of apertures in sa d mid-feather located near the bottom of said tank, a liquid circulating element located in each of said apertures, a plurality of backll ,back-falls being of different heights, whereby the liquid driven thru said apertures by said circulating elements will be directed upwardly and forwardly thru the central portion of said tank, and agitate the top surface of the liquid as well as other portions of the liquid in said tank.

2. A circular tank for materials in liquid form including a U-shaped mid-feather partition, a pair of apertures in said mid-feather located near the bottom of said tank, an impeller located in each of said apertures, means for operating each of said impellers, a pair of backfalls in the bottom of said tank located in front of said impellers, respectively, said back-falls being of different heights, whereby the liquid driven thru said apertures by said impellers will bedirected upwardly and forwardly thru the central portion of said tank, and agitate the top surface of the liquid as well as other por'tions'of the liquid in said tank.

3. A tank for materials in liquid form comprising a curved mid-feather" partition spaced from the outer wall of said tank, the distance between said mid-feather and the wall of said tank decreasing towards the center of said midfeather whereby to form two converging passageways of decreasing width between the tank wall and said mid-feather, an aperture in the center of said "mid-feather located near the bottom of said tank, a "back-fall on thebottom of said tank extending across the space within said mid-feather", said back-fall" extending above said aperture, means for impelling the liquid in said tank through said aperture and against said back-fall, the floor of said tank, within the space enclosed by said mid-feather, sloping downwardly from said "back-fall, and said downward slope of the tank floor continued in opposite direction in said converging passageways.

4. In a tank for materials in liquid form, a U -shaped "mid-feather" partition spaced from the outer wall of said tank, an aperture in the center of said mid-feather located near the bottom of said tank, a back-fall" on the bottom of said tank extending across the space within said mid-feather, the face of said back-fall" cpposed to said aperture sloping upwardly and extending to a height above said aperture, the opposite face of said back-fall" sloping downwardly to the bottom of said tank, and the floor of said tank between said mid-feather" and said back-fall sloping downwardly.

5. In a tank for materials in liquid form, a U-shaped mid-feather partition spaced from the outer wall of said tank, an aperture in the center of said mid-feather" located near the bottom of said tank, a back-fall on the bottom of said tank extending across the space within said mid-feather, the face of said back-fall" opposed to said aperture sloping upwardly and extending to a height above said aperture, the opposite face of said back-fall" sloping downwardly within the space inclosed by said midfeather to the bottom of said tank, and means for impelling the liquid in said tank thru said aperture and against said back-fall.

6. In a tank for materials in liquid form, a

.mid-feather partition, the ends of said midfeather partition spaced from the walls of said tank, an aperture in the center of said midfeather" located near the bottom or said tank, means for impelling the liquid in said tank thru said aperture, a back-fall" on the bottom of said tank located ahead of said aperture the face 01' said "back-tall" opposed to said aperture sloping upward beyond the height of the top of said aperture, the other face of said back-fall" sloping downward to the bottom of said tank, the bottom of said tank sloping downward from said back-fall".

GEORGE S. WITHAM, Jr. 

